# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Tests for L{twisted.internet.main}.
"""

from __future__ import division, absolute_import

from twisted.trial import unittest
from twisted.internet.error import ReactorAlreadyInstalledError
from twisted.internet.main import installReactor

from twisted.internet.test.modulehelpers import NoReactor


class InstallReactorTests(unittest.SynchronousTestCase):
"""
Tests for L{installReactor}.
"""

def test_installReactor(self):
"""
L{installReactor} installs a new reactor if none is present.
"""
with NoReactor():
newReactor = object()
installReactor(newReactor)
from twisted.internet import reactor
self.assertIs(newReactor, reactor)


def test_alreadyInstalled(self):
"""
If a reactor is already installed, L{installReactor} raises
L{ReactorAlreadyInstalledError}.
"""
with NoReactor():
installReactor(object())
self.assertRaises(ReactorAlreadyInstalledError, installReactor,
object())


def test_errorIsAnAssertionError(self):
"""
For backwards compatibility, L{ReactorAlreadyInstalledError} is an
L{AssertionError}.
"""
self.assertTrue(issubclass(ReactorAlreadyInstalledError,
AssertionError))